Add dataSetIds input to upload-action

[SgtPooki]

upload-action/action.yml exposes path, walletPrivateKey, network, minStorageDays, filecoinPayBalanceLimit, withCDN, dryRun but no way to target specific datasets. CI consumers cannot route uploads to existing datasets — every workflow run either creates a new dataset or reuses the action's own previously-created source=filecoin-pin ones via SDK smart-select. Storacha-migrated users running CI cannot append to their migration pair without forking or wrapping the CLI directly.

Add a dataSetIds input to action.yml. Map it to the existing executeUpload({ dataSetIds }) path used by the CLI's --data-set-ids flag (upload-action/src/filecoin.js:190).

Acceptance:

• dataSetIds: "13260,13261" in a workflow routes the upload to those datasets and skips creation.
• Omitted input preserves current behavior.
• Invalid input (non-numeric, mixed with providerIds if that ever surfaces) errors clearly.

Parent: #430
Investigation: https://gist.github.com/SgtPooki/d05e1ece2cdd9ae83ec003d2ec9e2979